If you bought them on steam, you will just need to reinstall Steam and redownload anything that you purchase on Steam.

Other ways of purchasing addons I suppose will depend on the vendors you bought them from. I personally make physical hardcopies of all my software purchases to CD and or DVD's for reinstalling later if need be, I'd advise you to do the same if possible.

If you bought them on steam, you will just need to reinstall Steam and redownload anything that you purchase on Steam.

Other ways of purchasing addons I suppose will depend on the vendors you bought them from. I personally make physical hardcopies of all my software purchases to CD and or DVD's for reinstalling later if need be, I'd advise you to do the same if possible.

By that was a quick reply!!
Can you make back ups from steam ? Where does it save the files to please ?

Viceroy, what I would do is "image" the old hard drive to the new one. Acronis True Image can do that perfectly. You won't have to reinstall anything. All your files will be saved, including Windows. (I am presuming you are just upgrading to a larger hard drive, tho)

If you are going to reinstall Windows (or upgrade) put the old hard drive on a secondary IDE (or SATA) channel, that way you can just copy over the "steamapps" folder once you reinstall Steam.

Any add ons that you buy, and already have installed, will be in the Railworks/ steamapps folder. If you find you have to reinstall any third party "stuff" you will need key codes from those particular vendors. Sux, but that's the way it is.